Adding a protection circuit to a CREE Flashlight

[Ajay]

Hello CPF folks! I wish to add a low voltage cut-off circuit to my Romisen RC-U4 cree light (http://www.dealextreme.com/details.dx/sku.11119). I have already bought the protection circuit module from :
http://www.batteryjunction.com/prcimopfor3l.html

I know these are designed to go on the negative terminal of the 18650 cell but I would rather add one to the flashlight instead of one every 18650 cell. I got all of my 18650 cells from a sony laptop battery pack so they are all unprotected (Sanyo UR18650F 2400mah cells).

1. Please point me to similar projects if they exist.
2. Where in the light would be the best place to put this circuit? Head or tail?
3. Is this a good or bad idea? Is it even possible?

Thanks:thinking:

 

[Ajay]

Well since nobody is responding to my post I went ahead and opened up the pill of my Romisen RC-U4. Here are the pics. I am very surprised at the amount of circuitry in the pill. I was expecting one circuit board not two. I am not sure what they are. I guess one is a buck boost board? If you know what they are please post.

Thanks
PS. Please excuse the dry skin

 

[jrmcferren]

It is not possible to add this PCB in your application. The positive lead of the battery goes to B+ the Negative lead goes to B-. The device (charger, load, or both) connects the positive to P+ and Negative to P-. There is no ground reference between the two sides. Don't get rid of the board, you may find another application for it.

 

[Marduke]

Why not just use protected cells to begin with? Using unprotected cells is rather dubious, both in the light and charging.

 

[jrmcferren]

Oh I didn't notice it earlier but your pictures are too big, the rules state no larger than 800x600 (or is it 800x800). Just a friendly reminder so a moderator does not pull them down and replace with links.

 

[Ajay]

Thanks for your response jrmcferren. I will use smaller pics next time. I see your point about the circuit but I think I can get it to work. I will monkey around with it and let you know how it goes...sometimes I gotta learn the hard way:shakehead.

Marduke I don't have protected cells and I am not going to buy any since I busted open two good laptop batteries and got 6x2400mah Sanyo UR18650 cells and 6x2600mah Sanyo from the other.
These are great cells and I didn't want to add protection circuits to each one. I would rather add them to the flashlight.
I also have a very good lipo changer that I trust to charge the cells without a problem...I never leave my cells while they are charging anyway.

 

[Ajay]

Ok. Images resized to 800x600.

 

[Lighthouse one]

I've had more protected cells go dead on me, than any thouble with unprotected cells that I use. I know it's preferable to use protected, but if you have good quality cells- and use just a bit of care with them- you will be fine. Lots of 18650's - and plenty of 123's too.

 

[Ajay]

Ok that's it! I give up :shakehead on trying to install a voltage cut off using this method.
Jrmcferren you were right!
This is a messy way to do this. I have been searching all over cpf and the web looking for other ways and I see that some flashlights already come with voltage cut offs or a warning system such as flashing when the cell voltage is low. Tiable ACE and A10 are examples of lights with such mechanisms built in.

Where can I get circuits that do the same? I searched dx and kaidomain and I have not found any.

Does anyone know where I can get circuit boards with cut off or warning mechanisms when the voltage is low on a single 18650?

This is frustrating...I know this stuff exists but why is it so hard to find?

 

[linterno]

Shiningbeam sells MG RX-1 Super Thrower 18650 Flashlight which has such a protection circuit (cut off at 2.7 v). Ask him if he can get one of those circuits for you.

 

[Ajay]

Thx Linterno, I asked Shiningbeam. No luck. He has none.

I will continue to search for a circuit board that will give warning or cut-off when the cell reaches 2.7 or 2.8v but until then I will try adding the protection circuit I got from batteryjunction.com to one or two of the 18650 cells.
Since I got no contact welder I will have to use a solder gun....man that's risky
I will let you guys know what happened if I live to tell.

HAPPY NEW YEARS TO ALL!!!

 

[Ajay]

Ok adding a protection circuit to a 18650 cell is nuts! I don't have the patience for it and I didn't have shrink tubing for the job so I canceled that part of the project. I am trying to keep the cost of this project very very low....recession low
Some good news: I found a circuit board at DX that apparently will cut-off at 2.6v. http://www.dealextreme.com/details.dx/sku.6190

So I just ordered 2 and I will install one in my Romisen and see if the cut-off works. If I had the money I would just buy a [FONT=&quot]JetBeam Jet-III PRO ST that already has a cut-off and is a high quality light. (I thought this light had cutoff but now I don't see this mentioned anywhere. I imagined it?)
[/FONT]

 

[Ajay]

Well I finally got the DX sku 6190 (3*7135 chips) and installed it in my Romisen RC-U4 (basically an Ultrafire c2). It does deliver close to 1amp to the LED when the 18650 is fully charged. The current and brightness does drop off as the voltage drops but still a good improvement over the stock driver.

Now about the so called cutoff of this board: It starts flashing about 1hz when the voltage drops to 2.7 but it does not cutoff at 2.6v like advertised. I ran the cell down to 2.5 just to be certain. It should be marketed as a low voltage warning and not a low voltage cutoff. In any case this is definitely better than nothing at all. I can now use my free unprotected laptop 18650 cells in my torch!

 

[linterno]

In fact, there is no cutoff in that driver. You get ~350ma theoretical regulation per 7135 chip (~1050ma in the driver) when the battery voltage is 3.2+ volt (according to datasheet). After that you will get direct drive with reduced current. I guess, if you leave the flashlight turned on then the battery will continue to be drained.

 

[Ajay]

In fact, there is no cutoff in that driver. You get ~350ma theoretical regulation per 7135 chip (~1050ma in the driver) when the battery voltage is 3.2+ volt (according to datasheet). After that you will get direct drive with reduced current. I guess, if you leave the flashlight turned on then the battery will continue to be drained.

Understood linterno , but I just didn't like that fact that DX advertised the board as having a 2.6v cut-off.

 

[Norm]

Understood linterno , but I just didn't like that fact that DX advertised the board as having a 2.6v cut-off.

2.6V is the lowest recomended operating Voltage, not related to protection.
Norm